I’m going to the blunt: A ketogenic diet is not a panacea. In fact, keto diets can be dangerous for some people. It’s not without risk, and the scientific research on the diet long term is somewhat sparse. How do you know if keto is dangerous for you? It’s critical to have a balanced discussion about ketogenic diets and explore the available research.
Ketogenic diets have been used therapeutically for over 100 years, but keto is really having a moment and becoming a fad. It’s easy to get swept up in the allure of weight loss, 6-pack abs, endless energy, and boosted brain power.
To be clear, I am not against the ketogenic diet per se! I have seen many wonderful benefits with keto, but I have doubts about the safety of the diet long term (say, for a period of years), and keto will not be the right diet for everyone. Certain people may experience adverse effects from a higher fat and/or lower carb diet due to their genetic makeup, current health status, or particular genetic mutations. There can be a dark side to keto; there are documented adverse reactions, and you need to be informed.
The ketogenic diet is a high fat, low carb, moderate protein diet. It’s been used historically to treat specific medical conditions, like epilepsy and diabetes. (source) When deprived of the glucose your body and brain require for energy, the body begins to burn stored fat, and the liver produces an alternative fuel called ketones. You can read exactly how keto works in my other post here.
People are attracted to the ketogenic diet because of its many benefits, including weight loss without hunger (and it does seem to work well for this, at least initially), crystal clear thinking, improved lipids, better energy, epilepsy treatment, and even a way to overcome type 2 diabetes. The ketogenic diet has been shown to produce beneficial metabolic changes in the short term. Along with weight loss, other benefits include improved insulin levels and reduction in blood pressure, cholesterol, and triglycerides. (source)
And we do have solid evidence showing that a ketogenic diet reduces seizures in children, sometimes as effectively or more than medication. Because of these neuroprotective effects, questions have been raised about the possible benefits for other brain disorders, but there are no human studies to support recommending ketosis to treat these conditions (Parkinon’s, Alzheimer’s, etc). (source) That’s not to say a ketogenic diet wouldn’t work for those diseases, though.
Long story short is that keto advocates say the body thrives better burning fat for fuel instead of carbs, which can leave you brain fogged and tired. In fact, you don’t even need carbs with all the fat to burn, they say! Eating carbs drives up insulin production, causing increased hunger and triggering the body to hold on to fat and suppress calorie burn. But when you replace carbs with fat, you’re not hungry, and fat magically melts away. With fewer carbs, your body also doesn’t produce as much insulin. (source) High insulin means diabetes and increased oxidation and fat storage.
NOTE: carbs include vegetables. All carbs are not bad. Everything that is not a protein or a fat is a carb.
And most people report feeling great on keto. The diet forces you to ditch processed, refined foods, simple carbs, and junk food. No sugar, booze, or Cheetos. And that single change is a good thing: You’re eating more whole foods. Keto encourages consumption of free-range animals and wild caught seafood, good fats, bone broths, organ meats, and fermented foods. But it’s still minimal carbs at around 30 grams per day total carbs or less (equivalent to one sweet potato) and no grains or legumes. Not everyone (especially women) does well on such a low carb plan.
NOTE: whether you track net or total carbs depends on you and your health goals. Net carbs are total carbs minus the fiber. Some people will be fine counting net carbs; others will need to count total carbs to get into ketosis. The reason why people use net carbs (aka available carbohydrates) is because of the assumption that fiber doesn’t affect blood sugar. However, this claim isn’t entirely accurate because it only applies to insoluble fibre which cannot be absorbed and has no affect blood sugar and ketosis. (source)
Here’s the thing though: some of those benefits, while they sound wonderful, are still hypothetical. For example, while the ketogenic diet does work for short term weight loss, WHY it works is still a hypothesis (see carbohydrate-insulin hypothesis). There are no long term studies and no solid evidence that keto diets are beneficial for weight loss and lipid improvements in the LONG TERM. (side note: I did find this recent study on a small group of obese patients following a very low calorie ketogenic diet over a period of 2 years. They had continued weight loss success, but I did not see any info on other health markers in the study. This also suggests that obese people would fare better on keto as long as they still have weight to lose and are using the diet for this purpose).
When I say long term, I mean following a ketogenic diet for more than 6 months. (this study does show keto’s beneficial effects over a period of 24 weeks for obese people). We just don’t have those studies yet. And that’s why people may experience wildly different results with keto for longer than, say 3 months (more on this later). Some animal research even points to potential problems like nonalcoholic fatty liver disease from long-term adherence to the diet (source).
The Dark Side of Keto
Truly, we are more confused than ever about macronutrients (protein, fat, and carbs) in the diet. Fats cause heart disease; no, sugar does; all carbs are bad; too much protein is bad for your kidneys. Want to know why we are confused about what diet works best and what we should eat? Because there is no universal correct answer about the perfect human diet.
Except maybe that we could all stand to eat more veggies (but there are even caveats to that).
Why? Well, we all have different physiologies; we all require different macronutrient ratios, and based upon our genetics and lifestyle, some of us have greater or lesser needs for things (like fat) than others. You may not get the same results feeding different humans an identical diet. Furthermore, we can’t do controlled studies on humans because we cannot lock them up in a lab. Therefore, accounting for control factors like stress levels and lifestyle habits that strongly influence outcome is impossible.
Back to keto. Same principle applies here: A ketogenic diet is not an ideal diet for some people. And it may not be an ideal diet long term for ANYONE. It may improve one’s insulin sensitivity in the short term, and it may accelerate fat loss and reduce inflammation, and it absolutely has benefits when used to treat epilepsy. But the ketogenic diet is a therapeutic diet. Think of it as a prescription that can be used temporarily to treat a condition until results are achieved. Long term keto can be a stressor on your adrenals and endocrine system.
Some researchers state that the ketogenic diet acts more as a drug than a diet because it emulates starvation and produces benefits to certain systems at the detriment of others (namely the endocrine system). (source)
In fact, in a recent study (one of the few long term studies of its kind) on carbs and longevity, new evidence suggests that neither high-carb nor low-carb diets are necessarily great for your health. Scientists studied more than 15,000 people in the US and another 432,000-plus around the world, and found that getting about 50-55% of a day’s energy from carbohydrates might be ideal for longevity. Conversely, people who derived more than 70% of their energy from carbs or got less than 40% of their daily calories from carbohydrates were more likely to die than people who ate something in between. Read all about it here.
Some of the only long term studies we actually DO have on the ketogenic diet are from tracking children who have seizure disorders. From these studies, we know with confidence that long term ketosis may pose substantial risk for health complications due to the side effects experienced by the thousands of children who have followed ketogenic diets over the years as a means of suppressing seizures unresponsive to drugs and procedures. Some of the side effects include stunted growth, kidney stones, heart issues, constipation. Read more here. Other documented adverse reactions of the ketogenic diet include serious illness and death. That’s why it’s a must to research this diet when using it in a therapeutic manner.
But if you feel so great on a keto diet and you’ve lost so much weight, how can it be bad? You gotta look under the hood to understand exactly how it’s working for you. By that I mean your gut function and blood work, specifically lipid panels and inflammatory markers (best measured via hs-CRP). Not all individuals will respond well to diets high in fat from animal sources like meat and dairy. You can find out if this is you by checking your blood every 6 months.
Request the following labs:
- Cholesterol (with an advanced panel that includes fractionated LDL and HDL)
- Fasting glucose and hemoglobin A1C (a three-month snapshot of blood glucose)
- Inflammation (C-reactive protein, homocysteine)
- Thyroid function (with an expanded thyroid panel, including TSH, free T3, reverse T3, free T4)
- Sex hormones (cortisol, estrogen, progesterone, testosterone)
- Electrolytes and minerals (sodium, potassium, magnesium, copper, zinc, selenium)
For example, a doctor colleague of mine mentioned the following:
“I have a patient who’s been on a ketogenic diet for 7 months. She lost 14 stubborn pounds of body fat, her brain is clear, and her carb cravings are gone. She wants to continue this plan, BUT her LDL cholesterol went from 119 to 253. Total cholesterol from 199 to 355. HsCRP from 0.21 to 3.0.”
If you don’t speak labwork, it means this person is showing a major spike in inflammation. It’s confusing because she feels great, but her body is showing a dramatic elevation in inflammatory markers like LDL and CRP. And these results are not uncommon in those on a ketogenic diet. It could be that this person doesn’t tolerate dairy, which may contribute to inflammation (keto diets encourage heavy cream and cheese); it’s too much animal fat for her physiology; or it’s not enough vegetables for her. After all, veggies and fruits are our highest antioxidant foods, and they are strictly reduced on a keto plan. Antioxidants squash inflammation and free radical damage.
Keto, Low Carb Diets, and Gut Bacteria
Fruits, veggies, and legumes also feed the beneficial bacteria in your gut, and we don’t know the long term effects of reducing the fibers and starches these bugs need to keep you healthy. (source) The ketogenic diet is low fiber because of the strict carb restriction, and many people suffer constipation as a result after transitioning to keto. Fiber deficiencies *may* harm our guts and the population of friendly bacteria, your microbiome.
Our gut bacteria modulate inflammation and immune response. High fat diets can adversely affect your beneficial gut bacteria. They need prebiotic fibers to thrive, and if they don’t get fed, they die. Reduced gut bug population could mean trouble in the long run; HOWEVER, other bacterial populations may bloom and thrive on a low carb diet. And if you become a healthier host as a result of your lower carb diet, you will see healthier bacteria grow. Conversely, if you feel terrible on a ketogenic diet and better on a diet with more fiber and vegetables, you will have healthier populations of gut bacteria and be healthier overall. So fiber content and resulting effects vary person to person.
And speaking of fiber, a large body of literature on centenarians (those who are 100 years old or older) shows that they often follow higher carb diets. Mind you, I’m not talking about bread and pasta and pizza, but detailed studies of centenarian diets show that over 80 percent of calories in their diet comes from vegetables, fruit, legumes, and complex carbohydrates, such as whole grains, brown rice, oats, and sweet potatoes. That’s a strong clue that the relationship between healthy carbs and fiber and the diet and longevity is a largely beneficial one. (source)
Side note: Whole grains won’t work for everyone, and I personally think humans fare better with lower grain and higher vegetable-based diets. I’m just citing the study above.
Check out my article on the Blue Zones (the areas with the highest numbers of healthy centenarians) for more on their diets, which all have one thing in common: On average, they’re 95 percent plant-based. This book (<–click link) on longevity research, fasting, and diet is fascinating also. Point is, longterm studies on the people who live the longest and are disease-free show their diets are not chronically high in fat and protein, but rather rich in all types of plant foods.
Another common effect of the ketogenic diet is the “keto flu”: fatigue, lightheadedness, and dizziness people feel when they suddenly and greatly reduce their carb intake to get into ketosis. This effect should go away after you adjust, BUT yet another doctor colleague of mine had a patient sent to the ER due to severe electrolyte imbalance during the keto flu phase (proponents of keto will tell you to take electrolyte supplements to ensure this doesn’t happen, and you should. Regardless, that risk is scary!). AND staying on keto for a long time may lead to kidney stones, liver issues, high cholesterol, constipation, slowed growth (in young people), and bone fractures. (source) This study shows that a high fat ketogenic diet caused insulin resistance in mice.
There’s not a single historic traditionally living human population that was in chronic nutritional ketosis. Even the Inuit, who mainly subsisted on fatty whale, seals, and fish, were not in chronic ketosis because they developed genetic mutations that prevented them from overproducing ketones. (source)
The Paleo Mom has an excellent article here documenting adverse reactions (unwanted or dangerous reaction) and supportive scientific literature on keto diet dangers.
Should I Try Keto?
So you’ve probably gathered that I don’t recommend a keto diet long term UNLESS you are monitoring your blood work and your markers look great. Even then, we still don’t know the long term effects of such a low carb diet on your organs (it’s potentially stressful for your liver to be producing ketones) or your gut flora, and those bugs literally make up more of you than your cells, so they’re pretty important for longevity.
According to Dr William Davis (author of Wheat Belly),
Short term, however (think 6 months or less), the diet can be very effective to help you reverse chronic conditions or jumpstart weight loss, especially if other methods aren’t working. You can use keto to reach your goals, then determine your ideal long term diet after your keto jump start.
There’s enough evidence that shows increased lipids are a known and predictable consequence of a ketogenic diet, so that’s a risk to consider. If you have epilespy or diabetes, or you’re obese, keto may be a great choice for you (how long depends on you). There’s even promising research on a ketogenic diet for cancer treatment.
There is even more controversy when considering the effect of keto on cholesterol levels, however. A few studies show some patients have an increase in cholesterol levels in the beginning, only to see cholesterol fall a few months later. However, there is no long-term research analyzing keto’s effects over time on diabetes and high cholesterol. (source) Note that high cholesterol is a sign of inflammation in the body.
A keto diet can be dangerous if you have certain health conditions (that you may not be aware of) such as
- kidney disease
- fatty liver
- low thyroid function, hypothyroidism
- adrenal fatigue or hormone imbalance
- women with irregular cycles
- history of eating disorders
I do not recommend keto for people with hypothyroid, adrenal/mitochondrial fatigue, or chronic constipation.
I also have doubts about how well women fare on keto. Women often don’t do well on such low carb diets, because we have very delicate endocrine systems designed for reproduction. Dr Sara Gottfried says, “My anecdotal observation in my medical office and working with people online is that men perform better in nutritional ketosis compared with women, particularly women aged 40 and older. My female patients, myself included, have more problems on keto with their stress hormones (i.e. producing too much cortisol), thyroid function, and may develop menstrual irregularities. At the root of these problems is dysfunction of the control system for hormones, the hypothalamic-pituitary-adrenal-thyroid-gonadal (HPATG) axis.” (source)
The body senses famine is ahead when deeply restricting carbs and responds by shutting down fertility (via thyroid function) because it’s not a safe time to reproduce. I’ve worked with many women who are recovering from trashed hormones from doing keto, and some studies indicate very low carb diets can affect thyroid hormone production and conversion. (source) That said, I have seen keto be an effective weight loss tool for post-menopausal women when used for 3 months or less (anecdotal), and it does seem to work well for PCOS, probably because it reverses the insulin resistance associated with this hormonal imbalance.
Dr Gottfried also notes that up to 45 percent of adolescent females have menstrual irregularities on the ketogenic diet. JJ Virgin also only recommends keto short term. (source)
Other questions to consider include the following:
- Do the benefits of the diet outweigh the risks with what you’re using it for?
- What are the long term health impacts from a high fat diet?
- How does a high fat, moderate protein diet impact long term kidney and liver function? Gall bladder?
- Is a ketogenic diet appropriate for women, or will it harm fertility, hormones?
- How long should children go keto to treat epilepsy?
- Do you have hypothyroid issues or Hashimoto’s?
If you’re considering keto, please monitor your cholesterol laboratory results to gauge inflammation (you can even order labs yourself via Direct Labs or EverlyWell). Ketogenic diets can work wonderfully for some people, but ask yourself is this diet right for me, and what do my labs show?
BOTTOM LINE: A ketogenic diet is a therapeutic diet that can be used to reverse health conditions like epilepsy, insulin resistance, obesity, diabetes, and even cancer. But it may not be safe long term, and not everyone will thrive on keto. Dr Gottfried also says, “There are at least ten genetic variations that may make a person less likely to benefit from keto.” (source) That’s quite fascinating, actually, as we enter into a era when we’ll have genetic testing available to tell us exactly which diets are genetically appropriate for us. No more guesswork.
Even Paleo/primal expert Mark Sisson says, Not everyone needs to be on a ketogenic diet. Even fewer need to be on a ketogenic diet for life. I’ll admit to being a bit leery of long-term, protracted ketosis in people who aren’t treating a medical condition. It just doesn’t seem necessary.” (source)
For certain folks, the ketogenic diet can be too much fat or too few carbs. Many health professionals, myself included, recommend using a ketogenic diet for a period of months (less than 6) until results are achieved, then reintroducing more healthy carbs such as veggies of all types, starchy root veggies, and legumes (if appropriate for you) and determining one’s carb tolerance for the long term. We need more studies and a thorough understanding of the pros and cons of keto before making generalized assumptions about it. No one single diet will be right for every person.
Mary Vance is a Certified Nutrition Consultant and author specializing in digestive health. In addition to her coaching practice, she offers courses to help you heal your gut and kick nagging digestive issues for good. Mary lives in San Francisco and Lake Tahoe in Northern California. Read more about her coaching practice here and her background here.